I am taking tamsulosin 0.4 for the last 5 days for the treatment of problem related to passing urine slowly and storage of urine in lower abdomen. by mistake i took 1 terazosin tablet 2 mg last night and feeling strong obstacle to pass the urine?

Like many antihypertensive meds, terazosin can cause some fluid retention, but it actually is used to treat men with bladder outlet obstruction, so your difficulty urinating would be a paradoxical reaction if terazosin caused it. Did you happen to take any medication like a nasal decongestant which can cause urinary hesitancy or obstruction of urine flow? If you can't pass urine go to the ER.

This error did not cause your symptoms. If it persists mention it to your doc. Good luck